import matplotlib.patches

ax = gca()
c = matplotlib.patches.FancyArrowPatch((0.2, 0.2), (0.5, 0.5), arrowstyle="->", mutation_scale=20.)
ax.add_patch(c)

a = matplotlib.patches.ArrowStyle.CurveA()
Path = matplotlib.path.Path
pth = matplotlib.path.Path( [[.3,.1],[.7,.5]], codes=[Path.MOVETO,  Path.LINETO])
a(pth,1,1)
